The major objective of this research is to investigate object concepts in autistic children. Categorization of objects as manifested in sorting, functional and symbolic use of objects in play, and sensorimotor behaviors thought to reflect object permanence will be observed. The abilities of autistic children will be compared with those of mentally retarded and normal children of comparable mental age. Furthermore, object use in play, natural settings, and experimental tasks will be related to the child's level of receptive and expressive language. The synchrony in categorization, object use, and verbal skills among autistic, retarded, and normal children will be compared. This research will allow us to determine the nature of the cognitive and language deficits associated with infantile autism.